Line an 8×8 pan with parchment so it’s overhanging on two sides. Spray with cooking spray.
In a saucepan, add the milk chocolate chips and 2/3 of a can of sweetened condensed milk. Over low heat, stir frequently until melted. Reserve 1/4 cup in a microwavable bowl and pour the remaining chocolate into the prepared 8×8 pan.
Add the Reese’s Pieces on top of the fudge and press gently.
Add the white chocolate chips and remaining 2/3 can of sweetened condensed milk to a saucepan and melt, stirring frequently, over low heat. Once melted, add the chopped Reese's Peanut Butter Cups and gently fold in. It’s okay if it the Reese’s melt a little; it will give the white chocolate a pretty swirl.
Pour the fudge on top of the milk chocolate layer already in the 8×8 pan. Sprinkle the Reese’s Minis on top and press gently.
Heat the reserved 1/4 cup of milk chocolate fudge in the microwave until it’s soft and add to a sandwich bag with a tip cut off. Squeeze on top of the fudge in the pan to create a drizzle.
Chill in the refrigerator for 1 hour or until set. Lift parchment to remove fudge from pan. Cut into squares and serve.